This invention is related to the field of optical switches and, in particular, to an optical switch containing nonlinear material.
Optical switches are known, however, the known optical switches generally do not have the desired degree of flexibility or do not have sufficient capacity for the uses to which optical systems designers would wish to put them.
For example, as will be described, U.S. Pat. No. 5,740,287 (Scalora et al.) represents an attempt to address some of the shortcomings of the known optical switches by including layers of nonlinear dielectric material in an optical waveguide. Scalora et al. discloses an optical switch in a one-dimensional multilayer dielectric stack in which at least every other layer of the stack is composed of a nonlinear dielectric material. The other layers are linear dielectric material. A transmission function for the stack disclosed by Scalora includes a photonic band gap, and a result of the structure of the stack is that the location and size of the photonic band gap varies with variations in the intensity of the incident light. However, in order for the stack to function, it should be designed for light having a frequency in the photonic band gap which is very near to the low intensity photonic band edge. Practical applications for the stack disclosed by Scalora therefore can be somewhat limited.
There is a continuing need for an optical switch which will have the necessary flexibility and capacity.
In one of its aspects, the invention provides an optical switch for operation by an incident light. The optical switch has a nonlinear grating portion and a linear grating portion. The nonlinear grating portion including a plurality of periodically alternating layers of a negative nonlinear material having a first nonlinear refractive index and a positive nonlinear material having a second nonlinear refractive index when the incident light has a first intensity, the first nonlinear refractive index being higher than the second nonlinear refractive index. The nonlinear grating portion has a first average nonlinear refractive index when the incident light has the first intensity, and the periodically alternating layers form a first nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices when the incident light has the first intensity. In addition, the nonlinear grating portion has a nonlinear grating period. The linear grating portion is positioned adjacent to the nonlinear grating portion, and the linear grating portion and the nonlinear grating portion meet at an interface. The linear grating portion includes a plurality of periodically alternating layers of a first linear material having a first linear refractive index and a second linear material having a second linear refractive index, the first linear refractive index being higher than the second linear refractive index. The periodically alternating layers comprising the linear grating portion form a linear grating portion sequence of alternating relatively higher and relatively lower refractive indices. Also, the linear grating portion has an average linear refractive index which is substantially equivalent to the first average nonlinear refractive index, and the linear grating portion has a linear grating portion period which is substantially equivalent to the nonlinear grating portion period. The nonlinear grating portion and the linear grating portion are positioned relative to each other so that the first nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, and in these circumstances, the incident light having the first intensity is substantially reflected. When the incident light has a second intensity, the negative nonlinear material has a third nonlinear refractive index and the positive nonlinear material has a fourth nonlinear refractive index. The second intensity is substantially higher than the first intensity. Also, the fourth nonlinear refractive index is substantially higher than the third nonlinear refractive index, so that the periodically alternating layers comprising the nonlinear grating portion form a second nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices when the incident light has the second intensity. The second nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by a discontinuity at the interface of the linear grating portion and the nonlinear grating portion, so that, when the incident light has the second intensity, the nonlinear grating portion has a second average nonlinear refractive index which is substantially equivalent to the average linear refractive index, and light having a narrow band of frequencies is substantially transmitted. In the result, when the incident light has the first intensity, the incident light is substantially reflected by the optical switch, and when the incident light has the second intensity, light having a narrow band of frequencies is substantially transmitted by the optical switch. In effect, when the incident light has the second intensity, the optical switch responds like a grating having a phase shift of xcfx80 between the linear grating portion and the nonlinear grating portion, and the optical switch transmits a narrow band of frequencies that are reflected at low intensities.
In another aspect, the invention provides an optical switch for operation by an incident light, the optical switch having a nonlinear grating portion, a linear grating portion, and a phase shift portion disposed between the nonlinear grating portion and the linear grating period. The nonlinear grating portion includes a plurality of periodically alternating layers of a negative nonlinear material having a first nonlinear refractive index and a positive nonlinear material having a second nonlinear refractive index when the incident light has a first intensity, the first nonlinear refractive index being higher than the second nonlinear refractive index. The nonlinear grating portion has a first average nonlinear refractive index when the incident light has the first intensity. In addition, the periodically alternating layers form a first nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices. The nonlinear grating portion has a nonlinear grating portion period. The linear grating portion includes a plurality of periodically alternating layers of a first linear material having a first linear refractive index and a second linear material having a second linear refractive index, the first linear refractive index being higher than the second linear refractive index. The periodically alternating layers comprising the linear grating portion form a linear grating portion sequence of alternating relatively higher and relatively lower refractive indices. The linear grating portion has an average linear refractive index. The linear grating portion also has a linear grating portion period which is substantially equivalent to the nonlinear grating portion period. The nonlinear grating portion and the linear grating portion are positioned relative to each other so that the first nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by a first discontinuity at the phase shift portion. The first average nonlinear refractive index is substantially equivalent to the average linear refractive index, and when incident light has the first intensity, light having a first narrow band of frequencies is transmitted. When the incident light has a second intensity, the negative nonlinear material has a third nonlinear refractive index and the positive nonlinear material has a fourth nonlinear refractive index. The second intensity is substantially higher than the first intensity. Also, the fourth nonlinear refractive index is substantially higher than the third nonlinear refractive index, so that the periodically alternating layers comprising the nonlinear grating portion form a second nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices when the incident light has the second intensity. The second nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by a second discontinuity at the phase shift portion, the second discontinuity differing substantially from the first discontinuity, so that, when the incident light has the second intensity, the nonlinear grating portion has a second average nonlinear refractive index which is substantially equivalent to the average linear refractive index, and light having at least one second narrow band of frequencies is transmitted by the optical switch. In the result, when the incident light has the first intensity, light having the first narrow band of frequencies is substantially transmitted by the optical switch, and when the incident light has the second intensity, light having the second narrow band of frequencies is substantially transmitted by the optical switch.
In accordance with another aspect of the present invention, there is provided an optical switch for operation by an incident light which includes a nonlinear grating portion, a linear grating portion, and a phase shift portion disposed between the nonlinear grating portion and the linear grating portion. The nonlinear grating portion includes a plurality of periodically alternating layers of a first negative nonlinear material having a first nonlinear refractive index and a second negative nonlinear material having a second nonlinear refractive index when the incident light has a first intensity, the first nonlinear refractive index being higher than the second nonlinear refractive index. The nonlinear grating portion has a first average nonlinear refractive index when the incident light has the first intensity. Also, the periodically alternating layers form a first nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices. The nonlinear grating portion has a nonlinear grating portion period. The linear grating portion includes a plurality of periodically alternating layers of a first linear material having a first linear refractive index and a second linear material having a second linear refractive index, the first linear refractive index being higher than the second linear refractive index. The periodically alternating layers comprising the linear grating portion form a linear grating portion sequence of alternating relatively higher and relatively lower refractive indices. The linear grating portion also has an average linear refractive index. In addition, the linear grating portion has a linear grating portion period substantially equivalent to the nonlinear grating portion period. The nonlinear grating portion and the linear grating portion are positioned relative to each other so that the first nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by a discontinuity at the phase shift portion. The first average nonlinear refractive index differs substantially from the average linear refractive index when the incident light has the first intensity, so that incident light having the first intensity is substantially reflected. When the incident light has a second intensity, the first negative nonlinear material has a third nonlinear refractive index and the second negative nonlinear material has a fourth nonlinear refractive index when the incident light has a second intensity. The second intensity is substantially higher than the first intensity. The fourth nonlinear refractive index is substantially higher than the third nonlinear refractive index, so that the periodically alternating layers comprising the nonlinear grating portion form a second nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices when the incident light has the second intensity. The second nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by the discontinuity at the phase shift portion, so that, when the incident light has the second intensity, the nonlinear grating portion has a second average nonlinear refractive index which is substantially equivalent to the average linear refractive index, and light having at least one narrow band of frequencies is substantially transmitted. In this embodiment, when the incident light has the first intensity, the incident light is substantially reflected by the optical switch, and when the incident light has the second intensity, light having at least one narrow band of frequencies is substantially transmitted by the optical switch.
In another alternative embodiment, the optical switch for operation by an incident light comprises a nonlinear grating portion, a linear grating portion, and a phase shift portion disposed between the nonlinear grating portion and the linear grating portion. The nonlinear grating portion includes a plurality of periodically alternating layers of a first positive nonlinear material having a first nonlinear refractive index and a second positive nonlinear material having a second nonlinear refractive index when the incident light has a first intensity, the first nonlinear refractive index being higher than the second nonlinear refractive index. The nonlinear grating portion has a first average nonlinear refractive index when the incident light has the first intensity. Also, the periodically alternating layers form a first nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices. The nonlinear grating portion has a nonlinear grating portion period. The linear grating portion includes a plurality of periodically alternating layers of a first linear material having a first linear refractive index and a second linear material having a second linear refractive index, the first linear refractive index being higher than the second linear refractive index. The periodically alternating layers comprising the linear grating portion form a linear grating portion sequence of alternating relatively higher and relatively lower refractive indices. The linear grating portion also has an average linear refractive index. The linear grating portion has a linear grating portion period which is substantially equivalent to the nonlinear grating portion period. The nonlinear grating portion and the linear grating portion are positioned relative to each other so that the first nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by a discontinuity at the phase shift portion. Also, the nonlinear grating portion has a first average nonlinear refractive index which differs substantially from the average linear refractive index when the incident light has the first intensity, so that incident light having the first intensity is substantially reflected by the optical switch. The first positive nonlinear material has a third nonlinear refractive index and the second positive nonlinear material has a fourth nonlinear refractive index when the incident light has a second intensity, the second intensity being substantially higher than the first intensity. The fourth nonlinear refractive index is substantially higher than the third nonlinear refractive index, so that the periodically alternating layers comprising the nonlinear grating portion form a second nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices when the incident light has the second intensity. The second nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by the discontinuity at the phase shift portion, so that, when the incident light has the second intensity, the nonlinear grating portion has a second average nonlinear refractive index which is substantially equivalent to the average linear refractive index, and light having at least one narrow band of frequencies is transmitted. In this embodiment, when the incident light has the first intensity, the incident light is substantially reflected by the optical switch, and when the incident light has the second intensity, light having at least one narrow band of frequencies is substantially transmitted by the optical switch.
In yet another of its aspects, the present invention provides an optical switch for operation by an incident light. The optical switch includes a nonlinear grating portion, a linear grating portion, and a phase shift portion disposed between the nonlinear grating portion and the linear grating portion. The nonlinear grating portion includes a plurality of periodically alternating layers of a first positive nonlinear material having a first nonlinear refractive index and a second positive nonlinear material having a second nonlinear refractive index when the incident light has a first intensity, the first nonlinear refractive index being higher than the second nonlinear refractive index. The nonlinear grating portion has a first average nonlinear refractive index n1 when the incident light has the first intensity. The periodically alternating layers form a first nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices. Also, the nonlinear grating portion has a nonlinear grating portion period P2. The linear grating portion includes a plurality of periodically alternating layers of a first linear material having a first linear refractive index and a second linear material having a second linear refractive index, the first linear refractive index being higher than the second linear refractive index. The periodically alternating layers comprising the linear grating portion form a linear grating portion sequence of alternating relatively higher and relatively lower refractive indices. In addition, the linear grating portion has an average linear refractive index n0. The linear grating portion also has a linear grating portion period P1 which is substantially greater than the nonlinear grating portion period P2. The nonlinear grating portion and the linear grating portion are positioned relative to each other so that the first nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by a discontinuity at the phase shift portion. When the incident light has a second intensity, the first positive nonlinear material has a third nonlinear refractive index and the second positive nonlinear material has a fourth nonlinear refractive index. The second intensity is substantially higher than the first intensity. The fourth nonlinear refractive index is substantially higher than the third nonlinear refractive index, so that the periodically alternating layers comprising the nonlinear grating portion form a second nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices when the incident light has the second intensity. The second nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by the discontinuity at the phase shift portion. The nonlinear grating portion has a second average nonlinear grating refractive index n2 when the incident light has the second intensity, so that the following equation:
2n0P1=2n2P2
is satisfied, and light having at least one narrow band of frequencies is transmitted. Also, 2n0P1 differs substantially from 2n1P2, so that the incident light having the first intensity is substantially reflected. In the result, when the incident light has the first intensity, the incident light is substantially reflected by the optical switch, and when the incident light has the second intensity, light having at least one narrow band of frequencies is substantially transmitted by the optical switch.
In yet another of its aspects, the invention provides an optical switch for operation by an incident light. The optical switch has a nonlinear grating portion, a linear grating portion, and a phase shift portion disposed between the nonlinear grating portion and the linear grating portion. The nonlinear grating portion includes a plurality of periodically alternating layers of a first negative nonlinear material having a first nonlinear refractive index and a second negative nonlinear material having a second nonlinear refractive index when the incident light has a first intensity, the first nonlinear refractive index being higher than the second nonlinear refractive index. The nonlinear grating portion has a first average refractive index n1 when the incident light has the first intensity. Also, the periodically alternating layers form a first nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices, and the nonlinear grating portion has a nonlinear grating portion period P2. The linear grating portion includes a plurality of periodically alternating layers of a first linear material having a first linear refractive index and a second linear material having a second linear refractive index, the first linear refractive index being higher than the second linear refractive index. The periodically alternating layers comprising the linear grating portion form a linear grating portion sequence of alternating relatively higher and relatively lower refractive indices. The linear grating portion also has an average linear refractive index n0. In addition, the linear grating portion has a linear grating portion period P1 which is substantially less than the nonlinear grating portion period P2. The nonlinear grating portion and the linear grating portion are positioned relative to each other so that the first nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by a discontinuity at the phase shift portion. When the incident light has a second intensity, the first negative nonlinear material has a third nonlinear refractive index and the second negative nonlinear material has a fourth nonlinear refractive index. The second intensity is substantially higher than the first intensity. The fourth nonlinear refractive index is substantially higher than the third nonlinear refractive index, so that the periodically alternating layers comprising the nonlinear grating portion form a second nonlinear grating portion sequence of alternating relatively higher and relatively lower refractive indices when the incident light has the second intensity. The second nonlinear grating portion sequence and the linear grating portion sequence form a continuous sequence of alternating relatively higher and relatively lower refractive indices along the optical switch, interrupted by the discontinuity of the phase shift portion. The nonlinear grating portion has a second average nonlinear refractive index n2 when the incident light has the second intensity, so that the following equation:
2n0P1=2n2P2
is satisfied, and light having at least one narrow band of frequencies is substantially transmitted. In addition, 2n0P1 differs substantially from 2n1P2, so that the incident light having the first intensity is substantially reflected. In this embodiment, when the incident light has the first intensity, the incident light is substantially reflected by the optical switch, and when the incident light has the second intensity, light having at least one narrow band of frequencies is substantially transmitted by the optical switch.
In yet another of its aspects, the present invention provides any of the described embodiments of the optical switch in which the optical switch additionally includes a gain medium for amplifying the incident light and a means for exciting the gain medium, so that when the incident light is supplied to the gain medium and the gain medium is excited; the gain medium amplifies the incident light.